Day 913

Friday.


1506.07523
Accurate and efficient halo-based galaxy clustering modeling with simulations
Zheng, Guo

Small- and intermediate-scale galaxy clustering can be used to establish the galaxy-halo connection to study galaxy formation and evolution and to tighten constraints on cosmological parameters.  With the increasing precision of galaxy clustering measurements from ongoing and forthcoming large galaxy surveys, accurate models are required to interpret the data and extract relevant information.  Introduce a method based on high-resolution N-body simulations to accurately and efficiently model the galaxy 2PCFs in projected and redshift spaces.  The basic idea is to tabulate all information of haloes in the simulations necessary for computing the galaxy 2PCFs within the framework of halo occupation distribution or conditional luminosity function.  It is equivalent to populating galaxies to DM haloes and using the mock 2PCF measurements as the model predictions.  Besides the accurate 2PCF calculations, this method is also fast and therefore enables an efficient exploration of the parameter space.  As an example of the method, decompose the redshift-space galaxy 2PCF into different components based on the type of galaxy pairs and show the z-space distortion effect in each component.  The generalizations and limitations of the method are discussed.


1506.07524
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses XV.  Assessing th achievability and precision of time-delay measurements
Bonvin, Tewes, Courbin, Kuntzer, Sluse, Meylan

COSMOGRAIL is a long-term photometric monitoring of gravitationally lensed QSOs aimed at implementing Refsdal's time-delay method to measure cosmological parameters, in particular H0.  Given long and well sampled light curves of strongly lensed QSOs, time-delay measurements require numerical techniques whose quality must be assessed.  To this end, and also in view of future monitoring programs or surveys such as the LSST, a blind signal processing competition named the Time Delay Challenge 1 (TDC1) was held in 2014.  The aim of the present paper, which is based on the simulated light urges from the TDC1, is double.  First, test the performance of the time-delay measurement techniques currently used in COSMOGRAIL.  Second, analyse the quantity and quality of the harvest of time delays obtained from the TDC1 simulations.  To achieve these goals, first discover time delays through a careful inspection of the light curves via a dedicated visual interface.  The measurement algorithms can then be applied to the data in an automated way.  Show that the techniques have no significant bases, and yield adequate uncertainty estimates resulting in reduced chi2 values between 0.5 and 1.0.  Prove estimates for the number and precision of time-delay measurements that can be expected from future time-delay monitoring campaigns as a function of the photometric signal-to-noise ratio and of the true time delay.  Make the blind measurements on the TDC1 data publicly available.


1506.07526
Redshift-space distortions in massive neutrino and evolving dark energy cosmologies
Upadhye, et al

Large-scale structure surveys in the coming years will measure the redshift-space power spectrum to unprecedented accuracy, allowing for powerful new tests of the LCDM picture as well as measurements of particle physics parameters such as the neutrino masses.  Extend the Time-RG perturbative framework to redshift space, computing the power spectrum P_s(k, mu) in massive neutrino cosmologies with time-dependent DE EoS w(z).  Time-RG is uniquely capable of incorporating scale-dependent growth into the P_s(k,mu) computations, which is important for massive neutrinos as well as modified gravity models.  Although changes to w(z) and the neutrino mass fraction both affect the late-time scale-dependence of the non-linear power spectrum, find that the two effects depend differently on the LoS angle mu.  Finally, use the HACC N-body code to quantify errors in the perturbative calculations.  For a LCDM model at z=1, the procedure predicts the monopole (quadrupole) to 1% accuracy up to a wave number 0.19h/Mpc (0.28h/Mpc), compared to 0.08h/Mpc (0.07h/Mpc) for the Kaiser approximation and 0.19h/Mpc (0.16h/Mpc) for the current state-of-the-art perturbation scheme.  The calculation agrees with the simulated redshift-space PS even for neutrino masses Sum m_nu~1eV, several times the current bound, as well as rapidly-evolving DE EoS, |dw/dz|~1.  Along with this article, make the z-space Time-RG implementation publicly available as the code redTime.


1506.07640
Precision cosmology with time delay lenses: high resolution imaging requirements
Meng, Treu,... Marshall, et al

Lens time delays are a powerful probe of cosmology, provided that the gravitational potential of the main deflector can be modeled with sufficient precision.  Recent work has shown that this can be achieved by detailed modeling of the host galaxies of lensed quasars, which appear as "Einstein Rings" in high resolution images.  Carry out a systematic exploration of the high resolution imaging required to exploit the thousands of lensed quasars that will be discovered by current and upcoming surveys with the next decade.  Specifically, simulate realistic lens systems as imaged by HST, JWST, and ground-based adaptive optics images taken with Keck or the Thirty Meter Telescope (TMT).  Compare the performance of these pointed observations with that of images taken by Euclid (VIS), WFIRST and LSST surveys.  Use as the metric the precision with which the slope gamma' of the total mass density profile rho_tot~r^{-gamma') for the main deflector can be measured.  Ideally, require that the statistical error on gamma' be less than 0.02, such that it is subdominant to other sources of random and systematic uncertainties.  Find that survey data will likely have sufficient depth and resolution to meet the target only for the brighter gravitational lens systems, comparable to those discovered by the SDSS survey.  For fainter systems that will be discovered by current and future surveys, targeted follow-up with be required.  However, the exposure time required with upcoming facilities such as JWST, the Keck Next Generation Adaptive Optics System, and TMT, will only be of order a few minutes per system, thus making the follow-up of hundreds of systems a practical and efficient cosmological probe.


1506.07831
How well can Charge Transfer Inefficiency be corrected?  A parameter sensitivity study for iterative correction
Israel, Massey, Prod'homme, Cropper, Cordes, Gow, Kohley, Margrraf, Niemi, Rhodes, Shot, Verhoeve

Radiation damage to space-based CCD detectors creates defects which result in an increasing CTI that causes spurious image trailing.  Most of the trailing can be corrected during post-processing, by modeling the charge trapping and moving electrons back to where they belong.  However, such correction is not perfect -- and damage is continuing to accumulate in orbit.  To aid future development, quantify the limitations of current approaches, and determine where imperfect knowledge of model parameters most degrade measurements of photometry and morphology.  As a concrete application, simulate 1.5e9 "worst case" galaxy and1.5e8 star images to test the performance of the Euclid visual instrument detectors.  There are two separable challenges: if the model used to correct CTI is perfectly the same as that used to add CTI, 99.68% of spurious ellipticity is corrected in the setup.  This is because readout noise is not subject to CTI, but gets over-corrected during correction.  Second, if the first issue is solved, knowledge of the charge trap density within Delta rho/rho=(0.0272±0.0005)%, and the characteristic release time of the dominant species to be known within Delta tau/tau=(0.0400±0.0004)% will be required.  This work presents the next level of definition of in-orbit CTI calibration procedures for Euclid.